1. Field of the Invention
The present invention relates to a control device for a vehicle that includes an electrically heated catalyst (EHC) and a method for controlling the vehicle.
2. Description of the Related Art
For example, Japanese Patent Application Publication No. 8-210127 (JP-A-8-210127) describes a device that prevents electric leakage in an EHC. An exhaust gas control apparatus for an internal combustion engine that is described in JP-A-8-210127 includes an upstream catalyst carrier with a heater function, a downstream catalyst carrier, and a bypass passage through which a portion of exhaust gases bypasses the upstream catalyst carrier and is guided to the downstream catalyst carrier. Accordingly, the temperature increase of the downstream catalyst carrier is promoted. In the above configuration, since a positive, electrode of the heater in the upstream catalyst carrier is positioned above the bypass passage, it is possible to prevent electric leakage that is caused by dew condensation water in the bypass passage that flows to the positive electrode.
In addition, for example, Japanese Patent Application Publication 8-338235 (JP-A-8-338235) describes a device in a hybrid vehicle. The device heats a catalyst when an electric power source for driving a motor needs to be charged in a situation where the motor is operated but an engine is not. The device then permits startup of the engine after a control unit determines that the catalyst has been heated to a temperature at which the catalyst is sufficiently activated.
Furthermore, for example, Japanese Patent Application Publication No. 2003-227366 (JP-A-2003-227366) describes a control device for a vehicle. In a hybrid vehicle, the control device energizes an EHC when the EHC is at low temperature, and starts up an engine even when the EHC is not activated as long as requested torque is equal to or larger than a specified torque.
Moreover, for example, Japanese Patent Application Publication No. 10-288028 (JP-A-10-288028) describes a hybrid vehicle in which an EHC is energized when an engine starts up due to a reduced state of charge (SOC) during a period when the vehicle is running in an electric vehicle (EV) mode.
Burnt gas in an internal combustion engine contains water as one of its components. Accordingly, when the internal combustion engine is left unoperated for a long period, dew is likely to be formed as a result of condensation especially in an exhaust passage of the internal combustion engine. Thus, when the internal combustion engine is started after such a relatively long unoperated period, the exhaust passage that includes the EHC is often subjected to a humid atmosphere. Specifically, in a vehicle with the EHC that is energized to promote heating of a catalyst, a favorable exhaust gas purification effect is easily obtained such as when the engine is started up from a cold state. Meanwhile, when the EHC is energized, a conductive state may be established between the EHC and the vehicle or between the EHC and the exhaust passage by condensed water, for example. Consequently, electric leakage may occur.
When the electric leakage occurs upon the energization of the EHC, or when the EHC is energized even in a situation where the electric leakage is likely to occur, a portion of electric power that is originally provided to heat the catalyst may be wasted. In addition, since the vehicle itself (i.e. a body or a chassis) or the exhaust passage can be electrically charged, a driver may get an electric shock by contacting the vehicle body while driving the vehicle, although a degree of shock may vary. Therefore, if the EHC is installed in the vehicle, it is essential to detect abnormality of the EHC.
In the device that is described in JP-A-8-210127, the electrodes are disposed in consideration of the possible electric leakage. However, such a measure in terms of hardware is insufficient to prevent the electric leakage or a crack in the exhaust passage that is primarily caused by the condensed water. In addition, since the device is developed on the basis of a technical idea that emphasizes prevention of an abnormality, it is difficult with the device to accurately detect the occurrence of the abnormality.
In the hybrid vehicle, and especially in a plug-in hybrid vehicle (PHV), an electric storage means such as a battery can appropriately be charged by an external electric power source. Thus, compared to a vehicle that only includes the internal combustion engine as a power source, the startup frequency of the internal combustion engine is significantly low in the hybrid vehicle or the PHV, and the internal combustion engine in the hybrid vehicle or the PHV is very likely to start from the cold state. For the above reason, an energizing request of the EHC may frequently be made, and a need for a measure to prevent the electric leakage may be significant. If the device that is described in JP-A-8-210217 is examined with the above issue in mind, the possible occurrence of the electric leakage is high in the hybrid vehicle in which dew is likely to be formed due to a lack of consideration that the device may be installed in the hybrid vehicle. With regard to the devices that are described in JP-A-8-338235, JP-A-2003-227366, and JP-A-10-288028, the EHC is adapted for use in the hybrid vehicle. In terms of exhaust gas purification, the technical idea to energize the EHC before and after a startup request of the internal combustion engine is made is beneficial. However, since such a technical idea is developed without any consideration of the electric leakage, it is impossible to prevent the electric leakage described above.
As it has been discussed so far, the above devices have a technical problem that it is difficult to prevent failure caused by the electric leakage if the EHC is installed in the vehicle. Needless to say, if only the prevention of the electric leakage is taken into consideration, the reduction in exhaust emissions upon startup of the internal combustion engine is not sufficiently achieved. In other words, failure that is caused by the electric leakage should be prevented without increasing the exhaust emissions.